Process of melting and degasifying metals under reduced pressure



Patented Sept. 29, 1925.

UNITED STATES WILHELM 30311. or HANAU, GERMANY.

PROCESS OF MELTING AND DEGASIFYING METALS UNDER REDUCED PRESSURE.

No Drawing.

Application filed Mar-ch 6, 1920. Serial No. 363,916.

(GRANTED UNDER THE PROVISIONS OF THE A0101 MARCH 3, 1921, 41 STAT. L,1813.)

'To all whom it may concern:

Be it known that I, WILHELM ROHN, a citizen of Germany, and resident ofHanan, Germany, have invented new and useful Improvements in Processesof Melting and Degasifying Metals Under Reduced Pressure, of which thefollowing is a specification.

It has been often suggested to melt metals under reduced pressure inseveral cases, and

this suggestion also has been executed but mainly for experimentalpurposes and in laboratories. It has also been tried to apply theresults obtained by such researches to practice, in particular for thepurpose of improving certain metals for special purposes. Heretofore,however, it has not been known that such experiments have led to apractical result in industry,'neither has it become known in trade thatmetals treated after such processes have been used on a commercialscale. The said experiments and researches have therefore well improvedscientific knowledge but have not advanced technical progress.

These failures were caused by the fact that the experiments were basedon an insufficient knowledge of the inevitable conditions of working andon inadequate knowledge of the physical and metallurgical properties ofthe metals to be treated.

By very extended and costly experiments and scientific research theinventor has extended considerably the knowledge in this direction andhas, by his invention, forming the subject matter of the presentapplication, rendered it possible to utilize the results of hisdiscoveries in practice.

For instance, the inventor has subjected soft commercialingot-iron tothenew meltin process. The technical improvement obtamed thereby willbecome apparent from the followin test results. The commercial ironshowe a Brinell hardness of 93. After having been remelted and submittedfor one hour to a pressure of 1 millimetre mercury column, the ironshowedaBrinell hardness of 72, after a second sample had been remeltedand submitted to the same pressure for a period of 3 hours, the Brinellhardness fell to 63. Before and after the meltingthechemical compositiondiffered but immaterially. I

Samples of the original material and of the second before mentionedmelting as well as of electrolytic iron melted according to theinvention were rolled and drawn into wire under exactly equalconditions. Forensuring absolutely unimpeachable results the drawing wasdone through a diamond drawing stone; the diameter was reduced from 1.9to 1.82 mm.

The original material required a force between 12 and 13 kilogrammes andthe remelted material a force between 9 and 10 kilogrammes. Theelectrolytic iron required a force between 8 and 9 kilogrammes. Theprocess, forming the subject 'matter of the present application thusrenders common commercial iron by a single melting almost equal to thehigh quality electrolytic iron as regards softness and ductility.

The present application relates to the general method according to whichit will be possible to produce metals of very superior qualities whichhitherto could not be produced in a. general commercial manner.Applicants co-pending applications, Serial Numbers 364,602; 364,603;365,321; 365,684 and Serial Number 432,308, induction furnace, describedthe novel manner in which this general method is used to produceentirely difi'erent metals and alloys of very. high purity andextraordinary chemical, physical and mechanical properties, and thelatter application described the novel furnace which enables thepractical and commercial working of the new processes described.

The present invention refers to metals, alloys of metals and theircompounds with metalloids, and is based on the recognition of thefollowing observation:

Until now the suggestions for melting under a vacuum proceeded from theidea of producing a certain vacuum in the melting furnace.

The vacuum was intended to prevent the formation of visible blow holesin ingots and castings and was also intended to withdraw the aii',whereby the oxidizing efi'ect.

of the oxygen was to be obviated.

This proposal did not consider that most metals and alloys expel besidesdissolved gases, also such gases which are formed uring the melting andthe heating, or during the cooling or even during solidification.

- a perfect vacuum, and that, in particular with gases which appear onlyat the solidification, it may be necessary to remelt the' metals twiceor three times, to ensure a complete withdrawing of the gas. It had notbeen considered that not only microscopicbut also microscopicallyascertainable gas inclusions and lastly also microscopically notascertainable, viz submicroscopical gas in clusions may to a wide extentdecrease the quality of the metals, and that therefore an industriallyuseful process should consider all these conditions.

If all these gaseous inclusions should be removed, a melting apparatushad to be designed, which would allow or provide any desired pressure inthe furnace and to maintain such pressure for any length of time, inother words, the melting apparatus must be practically absolutelygastight, as else it would be impossible to permanently maintain a givenvacuum, or to produce so high a vacuum, that also the submicroscopicalgas inclusions were removed.

The apparatus heretofore suggested for industrial purposes were notpractically perfectly airtight. The consequence was that in exhaustingthe air in allowably large quantities of air were sucked in through eventhe finest leaks, and this air unfavourably affected the meltingprocess.

Instead of excluding the injurious action of the oxygen of the air, thisaction was even increased. The intention, expressed in the hitherto madeproposals to exclude the air, besides securing the emerging of thedissolved gases could not be realized becausethe continually enteringfresh air continuously reacted on the metal bath and incessantly causedgases to be produced in the metal by metallurgical processes and to bedissolved therein. These incidents were until now notsufiicientlyrecognized, and were the reason, why all suggestionsheretofore made for melting metals and the like under reduced pressurehave not led to an industrial and commercial success.

The present invention consists primarily in submitting the metals to betreated to the -melting in a practically absolutely airtight meltingfurnace and at a constant reduced pressure which may vary from onethousand grammes per square centimeter to practically nil, accordin tothe purpose intended. The invention 1s, furthermore, based on thefollowing observation:

The suggestions heretofore made for melting in an evacuated furnace wererestricted to melting and heating the metals beyond theirmelting'points, and to exposing them thereupon or simultaneously to theinfluence of a lower or higher vacuum.

far as their properties when in molten state are not fully known, toascertain by experiment, at which temperatures gases are generated andat which temperatures dissolved gases are expelled. These temperaturesbeing ascertained the respective metal can be obtained continuously withthe same good qualities by treating it at the said temperatures. Forexample, an alloy of nickel and chromium which had been melted accordingto the process forming the subject matter of this invention at apressure of 1 mm.

mercury column and 1440 centigrade after previously showing a liberalevolution of gas remained quite calm and apparently free of gases. Whensubsequently worked, the metal showed bad qualities and tended to crack.The sams alloy being then melted at varying pressures and temperatures,it was found that at a. pressure of 3 mm. mercu column and a temperatureot 1460 centigrade a second, very violent emission of gas occurred. Theproduct of this melt was, on being worked, found to be perfect. All thenumerous alloys of the same composition melted since that time weremelted at 1460 centigra-de and 1-3 mm. mercury column pressure. They allhad a. second emission of gas and subsequently showed all the same,unexpectedly good qualities. 3 In all cases inwhich gases are emitted orproduced during the solidification the metal bath.must first be cooleddown to a temperature, at which the said gases are emitted. Thereuponthe metal should be remelt ed and the gases liberated be drawn off. Witha few metals and alloys it is cause a'further emission of gas. Only whensolidification sets in, a lively emission of gas commences and willcontinue until the alloy is fully solidified. An immediate remeltingwill showneither a further emission of gas during the meltin nor fromalloy of iron and cobalt for the large number the molten meal, but onlywill allow the escape of the mechanically included gases of the firstmelting. A renewed solidification liberates no more gas, and the productshows in every respect freedom of gas, flawless and goodsproperties.

The non-observance of the foregoing rules is responsible for the lack ofany practical results.

' The present invention consists therefore furthermore in firstascertaining for a given metal to be treated the temperatures which arenecessary to ascertain the desired effect whereupon the commercial andindustrial melting is carried out at the same temperatures.

This rule of working represents the best and most definite statement ofthe problem, because, on the one hand, every expert with some practicalexperience will be able to find the essential pressures and temperaturesfor any metal of interest to him, while, on the other hand, it isimpossible to name of metals, and above all the infinite number ofpossible alloys, which all show a more or less different behaviour,within the limits of .a patent application all their special propertiesand the rules and regulations covering them properl ft is obvious thatthe two aforementioned rules for working must be simultaneously appliedto all metals to be treated and that they supplement each other. It mustbe remembered that the emission of gas from the metal depends both onthe pressure-and on the temperature and that these two conditions cansupplement each other.

It is known both in science and in practice that an ascertainablecontent of gas in metals has had on their quality. It has been shown bycarefultests, that metals may also contain gases still higher degreewhich could previously not be ascertained andthat such gases will oftenunfavourably affect the quality of the .metals to a than theaforementioned gases. A process, which allows of removing from theirgases all gases from the metals milst therefore lead to a far reaching,heretofore never attained'imp'rovement in the quality of the formingvthe subject matter of the present application enables such completeremoval of all gases and represents therefore a highly importantindustrial and commercial improvement.

. This-importance is further increased by the fact that metals whichhave beenfreed through the present process will not again absorb gasesimpairing their quality even if they are again reheated for forging androlling purposes.

' What I claim is:

l; The process of melting and degasifying metal alloys and theircompounds wit an unfavourable influence metalloids, consisting inmelting these metals, under a reduced pressure in a practicallyabsolutely airtight furnace under a constant pressure of any valuebetween 1000 I .grammes per square centimeter and practically nil,according to the purpose intended and at a desired temperature, bothtemperature and pressure being made to act for a more or less long timeaccording to the properties of the components of the alloy andthereafter subjecting the melt to successively different constantpressures and dif-. ferent temperatures.

' '2. The process of degasifyin-g metals, metal alloys and theircompounds wit metalloids consisting in melting the metals hso under areduced pressure in a practically airtight furnace under a constantpressure of any value between one thousand grammes per square centimeterand practically zero and at a predetermined temperature, bothtemperature and pressure acting for a predetermined period, permittingthe melt to solidify and thereafter reheating said metals above themelting point to remove. further gases liberated during solidification.

3. The process of degasifying metals,

metal alloys and their compounds with metalloids, which consists inmelting the same in'a practically airtight furnace at a predeterminedconstant temperature and at a reduced constant pressure for apredetermined time interval, whereby to practically degasify such metal.

4. The process of degasifying metals, metal alloys and their compoundswith metalloids which consist in subjecting the melt to a firsttreatment in a practically airtight furnace involving predeterminedvalues of temperature and reduced pressure and thereafter subjecting themelt to a .metal alloys and their compounds with metalloids consistingin melting these metals under a reduced pressure, which pressure isconstant'and may be any value between one thousand grammes per squarecentimeter to second treatment involving predetermined values of temerature and reduced pressure,

practically zero and thereafter subjectigg 1 0 h the melt to' adifferent degree of redu pressure maintained constant for terminedperiod.

7 The process of degasifying metals, alloys and their compounds withmetalloids which consists in subjecting the melt to at least one meltingat a predetermined temperature and predetermined reduced pressure in apractically airti ht furnace, permitting the melt to solidi y andthereafter reheating the melt above the melting point to remove gasesliberated during solidification.

a prede- 8. A process for degasifying metals and the like consisting inmelting the metals in a practically air tight furnace at a predeterl Intestimony, that I claim the foregoing 20 as my invention I have signedmy name this 5th day of February, 1920.

DR. WILHELM ROHN.

